Transformer circuits



May 1s .1926. 1,585,018

W. L. CASPER ET AL TRANSFORMER CIRCUITSl Filed Jan. 2,5, 1924 Transmission in 800C`yce Miles Patented May 18, 1926.

UNITED STATES PATENT OFFICE.

WILLIAM L. CASPER, OF BROOKLYN, vANI) HORACE WHITTLE, Ol' NEW YORK, N.A Y.,

ASSIGNORS TO WESTERN -ELECTRIC? COMPANY, INCORPORATED, N. Y., A CORPORATION F NEW YORK. v

OF NEW YORK,

TRANSFORMER CIRCUITS.

Application led January 25, 1924. Serial No. 688,897.

This invention relates to the transmission of multi-frequency currents and has for its object to improve the uniformity of transmission of .such currents between circuits where one of the circuits has an' impedance having a substantial reactance component, particularly where this circuit is inductive.

In accordance with the invention, these cir- 'cuits which, for example, may b'e a resistance n circuit such as the output circuit of a three- 4electrode vacuum tube and an inductive circuit such as the circuit of an electromagnetic loud speaking receiver,y are connected by a transformerk having an impedance ratio equal to that of the interconnected circuits at a frequency to be transmitted. An ideal transformer, i. e. one having infinite mutual 'and self inductance `and no dissipative losses would give a maximum transfer of energyv at the frequency of impedance matching, with transmission losses at other frequencies, varying with the extent of variation of the ratio of actual impedances from the transformer ratio.

losses, one or more resonance conditions are established which have the effect of building up the voltage across the reactive circuit at the frequencies for which the losses are the greatest. In other words the reactance of 3 the reactive circuit is partially or completely annulled at these frequencies.

In onev form of the inventionfa capacity is connectedv across the circuit'which has a ositive impedance angle, the condenser belngin parallel resonance with the circuit at a frequency inthe intermediate portion of-the band to be transmitted` and causing. the circuit to have a negative impedance angle at the higher frequencies of the band. Since 4 the eiiciency of the circuit will be good at this frequency of resonance, the transformer connecting the two circuits is given an impedance ratio to match .the circuit impedance at some other intermediate frequency. The

transformer hhas associated with it effective series inductance, preferably inthe form o leakageinductance, which is given a value to resonate with the capacitative impedance of the reactive circuit near the u per end of the range to be transmitted, an a capaclty is `placed in series with a winding of the transformer, the capacity having a value to resonate with the inductive impedance of the In' order to `compensate for thesel reactive circuit as viewed throu h the transformer at a frequency near the ower end of the range. kWith this arrangement a more uniform transmission characteristic is obtained without introducing the losses which are caused by attenuation equalizers of types 6 show modifications o the invention, and

Fig. shows aphically. a transmission characteristic of t e circuit of Fig. 1.

Referring to the drawings by reference l numerals,the vacuum tube 10 of Fig. .1 which may be ofthe` usuall three-electrode type has its output circuit connected to a loud s eaking receiver 12 by a transformer 14.' T e impedance element' 15 which forms a by-path for direct current to the tube should have a sufciently high value that its effect on the tunin arrangements described below will be neg igible. A condenser 1 6 connected across the receiver has such a value that the impedance of the combination is inductive at the lower frequencies of the speech and music frequency range and capacitative at the upper frequencles of this range. The transformer 14 has an impedance ratio for matchin the output impedance of the tube to the impedance of the receiving circuit at a frequency somewhat above or below the frequenc at which the circuit 12, 16 isresonant. e transformer Ais designed to have leakage inductance, represented in the drawing by the dotted line elements 18 and 19. A condenser20 is provided in series with the primary winding 14.

The adjustment and operation of the circuit will be clearer from a consideration of Fig. 2- whichshows a circuit which is'equivf alent to that of Fig. 1. The vacuum tube 10 is represented in Fig. 2 by a source of multifrequency electromotive force 22 and a resistance 24. t The internal impedance of the vacuum tube is substantially constant with frequency and. may be approximately represented by a resistance. eglecting its dissipative characteristics, the transformer 14 may be represented by the T-network of inductances 25, 26 and 27, the inductances 25 this equivalent T-network the impedance of the circuit at one side ofthe transformer is considered to have been multipled by the impedance ratioof the transformer. The impedance of the loud speaker l2 may be represented approximately by an inductance 29 in parallel with va resistance ,30. The values Iof inductances 25 and 26 are such that they form with the capacity impedance of the circuit 16, 29, a circuit resonating near the upper end of the range to be 'transmitted. The frequency of resonance may be either within or without this range. The value of the mutual inductance 27 is high enough at this frequency that its impedance may be neglected. It may be pointed out here that an actual coil may be placed in a position of inductance 18 or 19 in which 'case the transformer may be designed to be substantially free from leakage inductance. The condenser 20 has a valve to form with the complete circuit to the right of the' condenser, a circuit resonant at a frequency near the lower end of the range. At this frequency the inductances 25 and 26 will have impedances low enough to be negligible while the inductance of the circuit will depend largely on the mutual inductance 27 and the inductance 29 of the receiver.

In Fig. 3, the transformer 32 matches the impedance of the vacuum tube which is again represented by the resistance 24 and that of the receiver represented by the elements 29 and 30 at a frequency in the intermediate portion of the speech and music range. The condenser 34 in parallel with the receiver is in resonance therewith at a frequency near the upper end of the range and a condenser 36 in series with the secondary Winding of the transformer forms a circuit comprising the mutual inductance of the transformer, condenser 36 and inductance 29 which is resonant near the lower end of the frequency range. The leakage inductance of the transformer may be made as low as is practicable.

In' Fig. 4, the transformer 38 is employed` having a ratio to properly match the interconnected impedances at a frequency near the upper end of the band to be transmitted. A condenser 40 forms a resonant circuit with inductance 29 and the inductance of the transformer at a frequency near the lower end of the band and a condenser 42 forms with the inductive impedance looking to the right a circuit which is also resonant at a low frequency. In this circuit, as in the circuit of Fig. 3, leakage inductance may or may not be present. v

In Fig. 5a transformer 44 matches the interconnected impedances at the lower end of the range to be transmitted and the condenser 46 is arran ed to form a parallel circuit with the inuctive i'mpedance to its right which is resonant at a frequency near the upper end of the band.

The circuit of Fig. 6 is similar to that of Fig. l-except that the series condenser 45 is placed in series with the secondary winding of the transformer 46 instead of in series with the primary and an actual inductance 47 is added to supplement the leakage inductance of the transformer. The values of the various elements may be adjusted to produce resonance points as in Fig'. l, that is, the circuit including condenser 45 and inductance 47, inductance 29 and the inductance of transformer 46 will be resonant at a frequencynear the lower end of the band, and the circuit including the leakage inductance, inductance 47 and condenser 48 will be resonant near the upper end of the range. The circuit may also be designed to operate in the manner of the circuit in Fig. 3, that is, the circuit 48. 29 will be resonant near the upper end of the range. In this case, the series circuit including the leakage inductance 47and capacity 48 as modified by the parallel inductance 29 will usually be resonant at a frequency far enough removed from the transmitted band that its effect will be negligible.

Referring to Fig. 7, in which the ordinates represent miles gain or loss and the abscisszc represent frequency on a logarithmic scale, curve A represents the loss which would occur if an ideal of fixed ratio transformer were to be used in the circuit 'of Fig. l having a ratio to match the interconnected impedances at 1,000 cycles as compared' with the transmission which would be obtained with a transformer of variable ratio which would match impedances at all frequencies. Curve B represents the transmission with the same transformer as considered incurve A, when provided with the condensers 16 and 20 and when the transformer has the required values of mutual and leakage inductance as specified above. As will be seen from a comparison of the two curves, the

transmission of the modified circuit is substantially uniform with frequency over a much wider range than that of the circuit using merely the ideal transformer. Furthermore, a net gain is obtained at all freuencies due to annulling the reactance of t e recelver.

What is claimed is:4

1. A transmission system comprisin two portions the impedance of one of Whic has a. substantial reactanC/e component, and means connecting said portions comprising a transformer having an impedance ratio equal to the ratio of the impedances of said portions at a frequency to be transmitted, said means comprising reactance forming masacre with the reactance of said reactive portion a circuit resonant at afrequency near a Widely different frequency to 'be transmitted.4

2. A transmission system comprising two portions the impedance of one of which has a substantial reactance component, and means connecting said p-crtionscomprising a transformer having an impedance ratio equal to the ratio of the impedance of said portions at a frequency to be transmitted, and said react-ive portion comprising a plurality of resonant circuits tuned at separated frequencies in or near a band to be transmitted, the voltage across one of the elements of each of said resonant circuits being also across said reactive portion.

3. A transmission system comprising two portions, the impedance of one of which has a substantial inductance component, and

a substantial inductance component, a condenser across said inductive portion and in said transformer forms with the inductance cf'said transformer and of said reactive porti-on a resonant circuit tuned at a frequency near the lower end of said band.

' 10. A system as in claim 8 in which a means connecting said portions comprising a y//condenser in series with the winding of said transformer having an lmpedance ratio/jl transformer which is inductively coupled to equal to the impedance ratio of said portions at a frequency to be transmitted said means comprising capacity resonant with the inductance of said inductive portion at a fiequency in or near a band tobe transmitted.

inductive portion.

6. A system as inclaim 3, which comprises anl additional capacity forming with said inductance a resonant circuit tuned at an. other frequency in or near said band.

7. A system as in claim 3, in which said means comprises inductance forming with said capacity a resonant circuit tuned atanother frequency in or near said band.

8. A transmission system comprising two portions, the impedance of `one of which has said reactive portion forms with thel inductance of saidtransformer and of said reactive portio-n a resonant circuit tuned at a frequency near the lower end of said band.

11. In combination, a three electrode vacuum tube, an electromagnetic receiver, a transformer connecting the output circuit of said tube and said receiver and having an impedance ratio equal to that of the interconnected impedances at a frequency in the speed and music range, and a plurality of capacities forming with the inductance of said receiver resonent circuits for increasing the amplitudes of frequencies in said range remote from said frequency.

In witness whereof, we hereunto subscribe our names this 24th day of January A. D., 1924.

WLLIAM L. CASPER. HORACE WHITTLE. 

